This invention is directed to a printed circuit card hole cleaner particularly for multilaminated printed circuit boards. The cleaner forces an abrasive slurry through the holes on the printed circuit board.
In the more complicated classes of printed circuit boards, at least three layers of conductor material, usually copper sheet, are separated by at least two layers of insulator material. The insulator is a glass fiber loaded epoxy material which has considerable mechanical strength. This board material has a surface to which the copper conductor layer can be securely attached. When it is desired to interconnect two or more of the printed circuit conductor layers, a hole is drilled through the board, completely through the conductor layers and the intermediate insulator board stock. It is intended that these holes will be plated through for the purpose of providing electrical continuity.
Residue is deposited on the walls of the holes as a result of the drilling action. The drill in its cutting action generates heat causing epoxy to soften and spread, thereby also displacing glass. The drill can also cause the epoxy and glass to be wiped across the conductor layer laminated within the board. The spread-on material adheres solidly to the conductor. This coating acts as an insulator. If it is not removed, it prevents the making of electrical connection to the interior conductor layer when plating through the hole is attempted. Thus, the interior of the hole must be cleaned so that through-hole plating can make successful and reliable contact with the interior conductor layer.
Prior attempts to clean printed circuit boards include the use of a vapor hone machine. This machine uses a pneumatic blast to carry abrasive grit to the printed circuit board to be cleaned. The pneumatic blast is applied from several inches away from the article to be cleaned. The vapor hone machine successfully cleans the surface and additionally deburrs and rounds the rims of the holes. Such rounding is helpful for successful through plating. However, the vapor hone machine does not adequately clean the internal surfaces of the holes. Thus, when using this machine, reliable through plating cannot be achieved.
The only satisfactory cleaning method previously discovered is the use of the chemical cleaning method. The chemicals to clean away smeared epoxy in the holes must necessarily be strong and thus chemical cleaning of the boards is dangerous. Thus, a reliable, safe inexpensive way of cleaning the through holes is required and has not been available until the advent of the printed circuit board hole cleaner machine of this invention.